Alternative reproductive strategies in the ruff, Philomachuspugnax: a mix ESS?
FREDRIK WIDEMO
Section of Animal Ecology, Department of Zoology, Uppsala University and Department
of Zoology, Norwegian University of Science and Technology, Trondheim
Sexual reproductive strategies tend to go unstudied amongst humans. That is,
there is not a large deal of research that has been collected on male strategies for mating
or copulating with a female that is territorially based. Recent evidence has shown
otherwise in animals. The study by Widemo (1996) seeks to find evidence of the
strategies that are most successful and overall which are most effective and efficient. The
species studied were certain breeds of the male ruff bird (or wader) located throughout
northern Eurasia.
The study focuses on leks or the gathering of males for the purpose of competitive
mating displays. In game theory an evolutionarily stable strategy (ESS), when played in
repeated “contests” over the long-term, cannot be “beaten” by any other strategy that
might be introduced (Mills). The study on a population of ruffs during breeding season
takes place between 1990-1997. The study analyzes reproductive success between the
Resident and Satellite strategies as well as between coupled and non-coupled Residents.
Within the species of ruffs, some males are referred to as Independents. According to
Widemo (1996) the goal of the study was to provide a detailed description of the
interactions between males adopting the two strategies and attempting to determine the
mating success of the strategies.
Independents attempt to establish and defend territories on leks. Others are
referred to as Satellites, which try to get access to territories defended by Independents.
Independents that succeed in establishing territories are called Residents (alpha male),
non-territorial Independents are called Marginals (seeks to be the alpha male), which are
potential future Residents that act as floaters. The status of Residents and Marginals
shows that there are transitions within the Independent strategy. Satellites are accepted
within Resident territory as long as they act submissively. Alternatively, Marginals are
chased to the outskirts of the leks. Typically, females visit Residents within their
territories and may or may not initiate copulation. If a Resident with a Satellite in its
territory is distracted, a Satellite may potentially steal a copulation.
Observed within the study are three evolutionarily stable strategies coded as
(Widemo, 1996): pure, conditional and mixed. A pure strategy consists of all individuals
adopting the same genetically fixed approach. Conditional strategies consist of several
approaches, which provide unequal fitness payoff and are adopted by individuals
depending on their competitive ability or status. Lastly, mixed strategies are different
strategies that coexist and award identical payoffs to the individuals adopting them. The
study focuses in particularly on conditional and mixed strategies, both genetically
determined male strategies.
Some of the major results discovered included females found inside the territories
of coupled Residents were found much more often than expected due to chance. The
presence of females increased Resident-Satellite couplings, and the absence of those
females resulted in decreased coupling. Also, more pecking recorded during the study at
the Satellite attracted more females. This may be due to dimorphism in their behavior that
was not present in Residents. In other words, Residents that did not peck as frequently as
Satellites tended to receive less attention from the females. The results found a positive
correlation between the number of females in a lek and number of Satellites.
Additional information within the study found that Residents copulate more when
coupled with Satellites and Satellites copulate almost exclusively when coupled with a
Resident. From 1990 to 1996 the percentage of copulations performed by Residents and
Satellites remained stable evidenced through the stability of both reproductive strategies.
Also, a positive relationship between the numbers of copulations performed while couple
and not coupled was found.
Widemo (1996) discussed that it is unclear whether Residents and Satellites
benefit from the presence of each other, whether the two strategies have equal fitness
payoffs and whether females sometimes prefer to mate with Satellites. A few
explanations for this have been argued. Satellites may track female movements on and
between leks. Satellites and females may prefer to visit the same Residents. Finally,
coupled Residents may enjoy more female visits because females prefer to visit coupled
pairs.
Ultimately, the Satellite strategy may represent a low-cost, low-benefit strategy
for both groups. In other words, both Independents and Satellites have similar success
even with different strategies. Different factors can affect lifetime reproductive success
such that Satellites and Independents may enjoy equal fitness payoffs even if one strategy
appears to copulate less.
Outline:
●
●
●
●
●
●
●
Abstract/Introduction (What is Evolutionarily Stable Strategies?)
Definition of a strategy
Types of strategies
○ Pure
○ Conditional
○ Mixed
Goal of study
Species
○ Independents
■
Residents (established territories)
■
Marginals (non-territorial)
○ Satellites
Male ruffs
○ Polymorphism (color)
○ Dimorphism (behavior)
Method
○ Study
■
Actions made by each group
●
●
●
●
●
Copulation attempts
○ Terminated copulation attempts
○ Disruptions
○ Successful
Monitoring (1990-1996)
Figure 2
Results (Interactions Between Male Strategies)
○ Maintenance of Male Strategies
Discussion
Test Questions:
1. A “satellite” gains access to a Resident’s lek by:
a. fighting him
b. submitting to him
c. sneaking in while the Resident is away
d. coupling with a female
2. Rank the order of copulation rate amongst male strategies from highest to lowest:
a) Marginal>Resident>Satellite
b) Resident>Marginal>Satellite
c) Resident>Satellite>Marginal
d) Satellite>Resident>Marginal
3. Which statement is TRUE regarding females and their effect on couplings:
a. Couplings on average last longer in presence of females
b. Satellites are less likely to leave in presence of females
c. Couplings are immediately terminated in cases when all females leave the
lek
d. All the above
e. None of the above
4. Both the Resident and Satellite must agree to form a coupling relationship.
a. True
b. False
5. Satellites are successful in copulation even when not coupled with a Resident.
a. True
b. False
6. Independent and Satellite copulation strategies often change in their lifetime.
a. True
b. False
Test Answers:
1) B
2) C
3) D
4) A
5) B
6) B